Blueberries are too! Coming from Maine...we like to hear that. Blueberries are a major source of flavonoids, in particular anthocyanins and flavanols. Although the precise mechanisms by which these plant-derived molecules affect the brain are unknown, they have been shown to cross the blood brain barrier after dietary intake. It is believed that they exert their effects on learning and memory by enhancing existing neuronal (brain cell) connections, improving cellular communications and stimulating neuronal regeneration.

Thanks for the article!

Nature always gives us the clue what is good for us and when.Foods that are red in color are good for increasing hemoglobin like beetroot,pomegranate,red banana etc. Similarly if one can carefully see the walnut it resembles like brain and it gives strength to the brain. All the foods like Amla(Indian gooseberry),Pistachio,Litchi,Mango ,Almonds,Walnuts etc.. which give strength to our brain are good for increasing concentration.
Apart from this certain other factors like constipation,blood sugar levels, physical activity,hemoglobin level plays important role in concentration.

Egg is good source of protein & nutrients, especially choline, egg yolk has good amount of choline which improves memory & learning capacity. Cranberry, fish, olive oil, oatmeals, sweet potatoes, lamb, spinach are excellent foods for concentration.